(1) Field of the Invention
The present invention relates to an optical pickup device capable of performing at least one of reproduction (playback), recording and erasure of information with respect to an optical disc (optical information recording medium) represented by a compact disc (CD) or a digital versatile disc (DVD). More particularly, the present invention relates to an optical pickup device that controls an output of a laser beam using a front monitor light receiving element.
(2) Description of the Related Art
FIG. 10 is a schematic diagram of a conventional horizontal arrangement-type optical pickup device using two light receiving and emitting integral-type elements 1a and 1b. In this optical pickup device, a laser beam emitted from each of the light receiving and emitting integral-type elements 1a and 1b and having an approximately horizontal optical axis 100 is transmitted or reflected by a beam splitter 12. The transmitted or reflected laser beam, which is transformed to a parallel beam by a collimator lens 13, is reflected approximately at a right angle in an upward direction, in which an objective lens 15 is present, by a raising mirror 14. The reflected laser beam is transmitted through the objective lens 15 and collected on a recording surface of an optical disc 16 that is arranged approximately horizontally.
The laser beam thus collected is reflected by the recording surface of the optical disc 16 and returned to each of the light receiving and emitting integral-type elements 1a and 1b via a reverse path to a forward path. This laser beam is then introduced onto a light receiving surface by a diffraction grating (not shown) provided on each of the light receiving and emitting integral-type elements 1a and 1b. An electric signal is detected according to a quantity of the laser beam received by the light receiving surface.
In such an optical pickup device, a part of the laser beam emitted from each of the light receiving and emitting integral-type elements 1a and 1b is directly made incident on a front monitor light receiving element 17 that is arranged approximately horizontally (i.e., approximately in parallel to the optical axis 100) in the vicinity of the beam splitter 12.
As shown in FIG. 11, the front monitor light receiving element 17 includes a substrate portion 20, a light receiving portion 21 fixed to a lower surface of the substrate portion 20, and a transparent resin mold portion 22 sealing the light receiving portion 21 to retain the portion 21 at a fixed position. This front monitor light receiving element 17 is arranged so that a light receiving surface (lower surface) of the light receiving portion 21 is approximately in parallel to the optical axis 100. The front monitor light receiving element 17 outputs the electric signal according to the quantity of the incident light, and controls an output of each of the light receiving and emitting integral-type elements 1a and 1b using an automatic power control (APC) circuit so that the laser beam collected on the optical disc 16 has an appropriate intensity.
The other conventional technique relating to the optical pickup device is disclosed in, for example, JP-A 2003-257064.
The optical pickup device configured as shown in FIGS. 10 and 11 has, however, the following disadvantages. The light receiving surface of the light receiving portion 21 of the front monitor light receiving element 17 is arranged to be approximately in parallel to the optical axis 100, and the quantity of the light incident on the front monitor light receiving element 17 is insufficient. It is therefore necessary to increase a control gain of the APC circuit. If the control gain is increased, however, a responsivity of the APC circuit is deteriorated. As a result, the optical pickup device cannot correspond to high-speed reproducing (playback) and high-speed recording of information from and to the optical disc represented by the CD or the DVD, and the optical pickup device may possibly be considerably degraded.